Topological transformations of phase diagrams of quaternary systems through the boundary tangential azeotrope stage

The specific features of quaternary system phase diagram transformations induced by formation ofboundary tangential azeotrope were investigated. The characteristics of bifurcation states corresponding to the transition from one structure of the diagram to another were determined. The principal possible transformations of diagrams with varying pressure were illustrated by the systems acetone-chloroform-ethanol-water and chloroform-ethanol-cyclohexane-water. The obtained results expand the understanding of thermodynamics of heterogeneous equilibria of multicomponent systems and make it possible to solve the practical problem of maintaining favorable phase equilibrium conditions for rectification in certain pressure ranges.